The process of preparing fibrous textile material for yarn manufacture includes a step of preparing a strand material known as roving. Roving is a relatively bulky and softly twisted strand of fibrous material in which the fibers have been generally aligned by a drafting process but which has not been attenuated to the extent typical in a yarn. The preparation of roving is accomplished by a textile machine known as a roving frame which has a plurality of drafting systems each of which receives one or more slivers and delivers a roving strand to a flyer, by which the roving is packaged by winding about a bobbin.
It has long been recognized that damage to a roving frame can result from the breakage or interruption of a roving strand intermediate a drafting system and a flyer. One form of such damage results from a "lap-up" of textile fiber about the delivery or front rolls of a drafting system. Further, such breakage of a roving strand can result in creation of textile fiber waste, which is undesirable for reasons of attaining manufacturing efficiency and quality.
It has been proposed heretofore that a roving frame may be provided with apparatus for sensing the interruption of roving delivery and stopping operation of the roving frame. One such apparatus is illustrated, for example, in Vehorn U.S. Pat. No. 3,309,859 issued Mar. 21, 1967. To any extent necessary to a clear understanding of the present invention, the disclosure of the Vehorn patent is hereby incorporated by reference into the present description. In the Vehorn control system for a textile roving frame, a plurality of sets of light sources and photoelectric detectors are provided, with each set viewing an area which extends longitudinally of the roving frame. The intended operation of the Vehorn control system, as disclosed in the aforementioned United States patent, is to stop operation of the roving frame upon interruption of any roving strand or runout of any sliver being supplied.
While the Vehorn control system has achieved acceptance, it is not capable of detecting a lap-up and, in its original form, encountered difficulty due to misalignment of roving frames. It has been discovered that such textile machines frequently are not properly aligned and that the flyers of such machines, if out of balance, will vibrate excessively. In any such event, a photoelectric receiver attempting to view a line or area extending lengthwise of a roving frame may respond to flyer vibration or misalignment, rather than to roving strand breaks. The roving operation is then subjected to false stops, in that the frame will be cut off when there is, in fact, no failure in proper operation of the frame. With the exception of lap-up detection, these difficulties have been avoided by recent Vehorn systems.
An alternative approach to a roving frame stop apparatus or stop motion device has been disclosed in Schneider et al U.S. Pat. No. 3,043,991 issued July 10, 1962. There, a plurality of individual detector units are arranged along the length of a roving frame, each monitoring a respective individual roving strand. To any extent necessary or appropriate to the understanding of the present invention, the disclosure to be found in the Schneider et al patent is hereby incorporated by reference into the present description. On first impression, an individual end detection device or unit as disclosed by Schneider et al U.S. Pat. No. 3,043,991 appears to overcome a number of the difficulties of the Vehorn type control system. Indeed, an individual end detector system does have certain capabilities, as pointed out more fully hereinafter, distinctive from those which can be accomplished by a control system of the Vehorn type. However, the Schneider et al stop motion device and control circuit therefor suffers from certain shortcomings, difficulties or deficiencies which have led to a failure of commercial acceptance of the Schneider et al arrangement. More specifically, the misalignment and vibration mentioned above in describing certain of the difficulties of a Vehorn control system cause "dancing" or vibrating motion of roving strands passing through a Schneider et al individual end detector. Such motion of a roving strand presents an initial alignment difficulty for a Schneider et al individual end detector, in that the roving strand does not predictably remain in a specific location, and may cause false stops. Further, alignment of the individual end detector devices of Schneider et al is difficult to accomplish reliably, particularly in view of the probable need of moving the device in order to accommodate doffing or removal of filled bobbins and in order to accommodate piecing up or reinstitution of roving packaging.